1. Field of the Invention
One embodiment of the present invention relates to a semiconductor device. Specifically, one embodiment of the present invention relates to a semiconductor device capable of obtaining and compressing imaging data.
In this specification and the like, the term “semiconductor device” generally means a device that can function by utilizing semiconductor characteristics. An imaging device, a display device, an electro-optical device, a semiconductor circuit, and an electronic device include a semiconductor device in some cases.
2. Description of the Related Art
Increases in the resolution and the number of pixels of a display device have been demanded; for example, an 8K ultra high definition television (UHD TV) with 7680 horizontal pixels by 4320 vertical pixels has been suggested. As the number of pixels increases, a size of the imaging data obtained by an imaging device also increases.
When an imaging data obtained by an imaging device is sent to other devices, the data is sent after being compressed, to reduce the data load in transmission. A typical data compression method in the case of motion image data includes an MPEG format. MPEG format utilizes discrete cosine transform on an imaging data in a referential frame which occurs every few frames, and in the frames between referential frames, discrete cosine transform is performed on the difference data between the imaging data of the referential frame and the imaging data of the frames between the referential frames.
A technique by which a transistor is formed using a semiconductor thin film formed over a substrate having an insulating surface has been attracting attention. The transistor is used in a wide range of electronic devices such as an integrated circuit (IC) and a display device. A silicon-based semiconductor is widely known as a semiconductor material that can be applied to the transistor, but an oxide semiconductor (OS) has been attracting attention as an alternative material. For example, a technique for forming a transistor using zinc oxide or an In—Ga—Zn-based oxide semiconductor as an oxide semiconductor is disclosed (see Patent Documents 1 and 2).
A transistor which includes an oxide semiconductor in a channel formation region (hereinafter referred to as an OS transistor) is known for its extremely low off-state current. Patent Document 3 discloses a technique in which a memory device is formed by using such off-state current characteristics. Patent Document 4 discloses an image sensor in which OS transistors are used.